1. Field of the Invention
The invention relates to an improved pump unit for a hydraulic vehicle brake system.
2. Description of the Prior Art
One pump unit, known from German Patent DE 198 09 571 C1, unit has an electric motor as well as a pump that can be driven with the electric motor. The pump of the known pump unit is embodied as a radial piston pump. The known pump unit has a rotor shaft, which is driven to rotate by the electric motor and which drives the pump. The rotor shaft is embodied as a hollow shaft. On an end remote from the pump, the rotor shaft is supported rotatably in a motor housing of the electric motor. An end toward the pump of the rotor shaft embodied as a hollow shaft is press-fitted, in a manner fixed against relative rotation, into an eccentric bush of the pump. The eccentric bush has a bore with which it is pressed, protruding axially, onto the end toward the pump of the rotor shaft. An outer circumferential face of the eccentric bush is cylindrical, and the cylinder is axially parallel and eccentric to the bore of the eccentric bush. On the outer circumference of the eccentric bush, there is a bearing on whose circumference the pump piston or pistons of the piston pump rest. When the motor shaft is driven to rotate, the eccentric bush rotating with it drives the pump pistons into a reciprocating motion for pumping fluid, in the manner known per se for piston pumps. For rotatably supporting the rotor shaft, a bearing is disposed in the bore of the eccentric bush. This bearing is disposed in the axial extension of the hollow shaft. The bearing is braced on a fixed cylindrical rod that penetrates the rotor shaft embodied as a hollow shaft. The cylindrical rod is retained in a manner fixed against relative rotation, outside the ends of the rotor shaft, in a pump housing and in the motor housing. There is a radial gap between the rotationally fixed rod and the rotatable rotor shaft embodied as a hollow shaft. By way of the press-fitted eccentric bush, which is supported rotatably on the pin by the bearing, the hollow shaft is supported rotatably on the end toward the pump.
The known pump unit has the disadvantage of being complicated and expensive to produce and manufacture. Another disadvantage is that in the region of the pump pistons, two bearings are disposed one inside the other, namely the bearing in the eccentric bush and the bearing disposed on the outside of the eccentric bush, making a radially large installation space necessary. Moreover, the rotationally fixed rod must protrude axially beyond the rotor shaft embodied as a hollow shaft, so that the rod can be secured. As a result, a great axial length of the pump unit is necessary.
International Patent Disclosure WO 94/27045, in FIGS. 1 and 8, discloses at least a pump unit for a hydraulic vehicle brake system with an electric motor, which has a cup-shaped motor housing and a housing cap inserted into it, and having a pump which is drivable by the electric motor and is accommodated in a pump housing; the pump unit has a rotor shaft, which extends from the motor housing through the housing wall and into the pump housing and is supported by means of a ball bearing, whose outer ring is located on one side in the housing cap and on the other in the pump housing. According to FIG. 1, the housing cap is of plastic and is designed such that essentially one-fifth of the length of the outer ring of the ball bearing can be press-fitted in, for the sake of positionally securing the outer ring. The remaining length of the outer ring of the ball bearing, upon the joining of the electric motor to the pump housing, can be inserted into a second stepped bore present in the pump housing. Because of the stepped bores, axial stops for the outer ring of the ball bearing are still available. In terms of its object, this construction has the advantage that the electric motor is in a complete state before it is united with the pump housing and can therefore be subjected to a test operation. Only if this test operation has proceeded satisfactorily is the intrinsically complete electric motor united with the pump housing and thus with the pump. Since the test operation can be performed in such a way that there is less radial stress on the ball bearing than in the later pumping operation, the housing cap is made from plastic. To enable the brush holders, accommodated on the housing cap and thus inside the cup-shaped motor housing, to extend as close as possible to a boundary plane of the pump housing on the cap end and nevertheless enable the outer ring of the ball bearing to be held sufficiently firmly for a test operation of the electric motor, the plastic housing cap is embodied with a greater thickness in one region around the outer ring of the ball bearing, and this thicker region is installed in an indentation that originates on a side of the pump housing toward the motor. The outer ring of the ball bearing, which is press-fitted into the housing cap on one side and on the other is insertable into a stepped bore of the pump housing serves upon insertion as a centering means for orienting the housing cap together with the electric motor relative to the pump housing. In the exemplary embodiment of FIG. 8 of WO 94/27045, an outer ring of the ball bearing protrudes with its part of its length out of the pump housing. Thus an indentation shown in FIG. 1, into which the thickened portion of the housing cap plunges, is omitted. In this respect, less machining expense is necessary for the pump housing of FIG. 8.
In a pump unit known from International Patent Disclosure WO 98/17514, an outer ring of a ball bearing is inserted with the majority of its length into a bore step located in the pump housing. The shorter portion of the length of the outer ring extends between attachments, which are located on the face end of a housing wall of the electric motor and are oriented toward a bore step that precedes those into which the outer ring of the ball bearing can be inserted. As a result, as soon as the outer ring of the ball bearing is inserted into the lower-lying bore step of the pump housing, it likewise serves as a means for aligning the electric motor relative to the pump housing. A motor shaft of the pump unit is embodied, adjoining the ball bearing, as an eccentric element located in the pump housing. A needle bearing surrounds the eccentric element, and bearing needles disposed around the eccentric element are encased by a bearing ring, and because of the closeness of the eccentric element to the ball bearing, the bearing ring can run up on an inner ring of the ball bearing. The housing cap is again made from plastic, is embodied as essentially platelike, and therefore dips into a depression that originates at a boundary face, toward the electric motor, of the pump housing and extends in the direction of the bore step associated with the outer ring of the ball bearing. Once again, the outer ring of the ball bearing, during its insertion into the associated bore step, serves as a means for orienting the electric motor relative to the pump housing. Because of the platelike embodiment of the housing cap, brushes of the electric motor are tangent to the boundary plane toward the motor of the pump housing. As a result, the cup-shaped motor housing is advantageously embodied as shorter than the length of the complete electric motor.
Other pump units for a hydraulic vehicle brake system are known from German Patent Disclosures DE 198 05 003 A1 and DE 198 49 669 A1, each having an electric motor that has a cup-shaped motor housing and a housing cap inserted into it; each pump unit has a rotor shaft, which extends from the motor housing through the housing cap and into a pump housing and is supported by a ball bearing, whose outer ring is located on one side in the region of the housing cap and on the other in the region of the pump housing. As a result, each housing cap is produced from sheet metal by deep drawing and/or stamping in such a way that pointing outward away from the interior of the motor housing, the housing cap has a tubular stub, which forms a bearing seat for receiving an outer ring of a ball bearing. The outer ring is press-fitted into the bearing seat for the sake of securing it against displacement in axial directions. Beginning at a respective face, toward the housing cap, of the pump housing, there is an opening in the pump housing whose diameter is larger than the outer diameter of the tubular stub that forms the bearing seat. Only in the event that a given rotor shaft is supported at three places, for instance as in FIG. 1 of DE 198 05 003 A1 or FIG. 2 of DE 198 49 669 A1, is the intrinsically complete electric motor orientable relative to the pump housing and thus to the pump in a technologically simple way, thanks to the third bearing.
In DE 198 05 003 A1, the housing wall is provided with a support, protruding counter to the pump housing, radially outside the opening in the pump housing that surrounds the bearing seat. For the sake of flush contact by frictional engagement of the protruding support, the housing cap is clamped against the pump housing by elastic deformation. This purpose is served on the one hand indirectly, via one end of the motor housing to be fastened, by fastening means of the kind that also clamp the cup-shaped motor housing against the pump housing. The clamping with elastic deformation of the housing cap is one provision for reducing noise.
In the example of the aforementioned DE 198 49 669 A1, the bearing seat, embodied in the form of a tubular stub, has a circular-annular face end, oriented toward the pump, which in this example is flush with a boundary plane of one face end of the outer ring of the ball bearing, which ring is press-fitted into the bearing seat. In this construction, the outer ring of the ball bearing is held by frictional engagement with a press fit in the bearing seat in two axial directions.